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At least 1,639 records · Page 91Linked to original sources
USGS2017

Geologic field trip guide to Mount Mazama and Crater Lake Caldera, Oregon

Crater Lake partly fills one of the most spectacular calderas of the world—an 8 by 10 kilometer (km) basin more than 1 km deep formed by collapse of the Mount Mazama volcano during a rapid series of explosive eruptions ~7,700 years ago. Having a maximum depth of 594 meters (m), Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 square kilometers (km 2 ) of pristine forested and alpine terrain, including the lake itself, and virtually all of Mount Mazama. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama’s climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest United States, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. In addition, many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama provide information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive processes revealed by geologic research at Crater Lake have been incorporated not only in scientific investigations elsewhere, but also in the practical evaluation of local hazards (Bacon and others, 1997b) and geothermal resources (Bacon and Nathenson, 1996). The 1:24,000-scale geologic map of Mount Mazama and Crater Lake caldera (Bacon, 2008) is unusual because it portrays bedrock (outcrop), surficial, and lake floor geology. Caldera wall geology is depicted in detail on the accompanying geologic panoramas, and bedrock geology is shown in a 1:50,000-scale geologic map. This field guide supersedes earlier geology guides of Crater Lake (Bacon, 1987, 1989).

Oregon↗
USGS1999

Water resources of Monroe County, New York, water years 1989-93, with emphasis on water quality in the Irondequoit Creek basin: Part 2. Atmospheric deposition, ground water, streamflow, trends in water quality, and chemical loads to Irondequoit Bay

Irondequoit Creek, which drains 169 square miles in the eastern part of Monroe County, has been recognized as a source of contaminants that contribute to the eutrophication of Irondequoit Bay on Lake Ontario. The discharge from sewage-treatment plants to the creek and its tributaries was eliminated in 1979 by diversion to another wastewater-treatment facility, but sediment and nonpoint-source pollution remain a concern. This report presents data from five surface-water sites in the Irondequoit Creek basin. Irondequoit Creek at Railroad Mills, East Branch Allen Creek, Allen Creek near Rochester, Irondequoit Creek at Blossom Road, and Irondequoit Creek at Empire Boulevard, to supplement published data from 1984-88. Data from Northrup Creek, which drains 11.7 square miles in western Monroe County, provide information on surface-water quality west of the Genesee River. Also presented are water-level and water-quality data from 12 observation-well sites in Ellison and Powdermill Parks and atmospheric-deposition data from 1 site (Mendon Ponds). Concentrations of several chemical constituents in streams of the Irondequoit Creek basin showed statistically significant trends during 1989-93. Concentrations of total suspended-solids and volatile suspended-solids in Irondequoit Creek at Blossom Road decreased 13.5 and 12.5 percent per year, respectively, and those at Empire Boulevard decreased 33.5 and 22 percent per year, respectively. Concentrations of ammonia plus organic nitrogen increased 17.6 percent per year at one site in the basin, but decreased 8.5 and 22.3 percent per year at two sites. Nitrite plus nitrate decreased at only one site (3.5 percent per year). Concentrations of total phosphorus increased at two sites (about 7 percent per year) and decreased at two other sites (7.6 and 29.9 percent per year), and orthophosphate concentrations increased at one site (10.8 percent per year). Dissolved chloride increased at three sites (1.7 to 10.9 percent per year), and dissolved sulfate decreased at one site (2.1 percent per year) and increased at one site (6.8 percent per year). Median concentrations of constituents were significantly lower in atmospheric deposition than in streamflow, although annual deposition of ammonia nitrogen, nitrite plus nitrate, total phosphorus, and orthophosphate in the basin exceeded the amounts removed by streamflow. Atmospheric deposition of chloride and sulfate, by contrast, represented only 1 and 12 percent, respectively, of the loads transported by Irondequoit Creek (Blossom Road site). Comparison of water-quality data from the Allen Creek site and Irondequoit Creek at Blossom Road from water years 1989-93 with corresponding data from 1984-88 indicates significant changes in median concentrations of several constituents. The concentration of dissolved chloride increased at Blossom Road and was unchanged at Allen Creek, whereas sulfate decreased at both sites. Concentrations of ammonia plus organic nitrogen, and nitrite plus nitrate, were significantly lower during 1989-93 than during 1984-88 at both sites. Total phosphorus concentration was lower during 1984-88 than during 1989-93 at Blossom Road but showed no change at Allen Creek, and orthophosphate concentration for 1989-93 was lower than in 1984-88 at both sites. Comparison of chemical loads in atmospheric deposition also indicates significant changes in many constituents. Five-year-mean loads of sodium, sulfate, and lead in atmospheric deposition for 1989-93 exceeded those for 1984-88, whereas 5-year-mean loads of calcium, magnesium, potassium, chloride, nitrite plus nitrate, ammonia nitrogen, and orthophosphate for 1989-93 were lower than in 1984-88. The changes in surface-water quality resulted from several factors within the basin, including land-use changes, annual and seasonal variations in streamflow, and year-to-year variations in the application of deicing salts on area roads. Statistical analyses of long-term (9 years or more) flow records of three unregulated streams in Monroe County indicate that annual mean flows for water years 1989- 93 were in the normal range (20th- to 80th-percentile). The greatest mean annual flow in this period-about 140 percent of normal at Irondequoit Creek and Black Creek-occurred in 1993, but the annual mean flow for that water year at Allen Creek was only 98 percent of normal. The lowest annual mean flows of these streams-ranging from 75 percent of normal to 93 percent of normal-occurred in 1989. The average annual mean flows for these streams for 1989-93 was 104 percent of normal, and that for 1984-88 was normal.

New York↗
USGS2000

Sources, instream transport, and trends of nitrogen, phosphorus, and sediment in the lower Tennessee River basin, 1980-96

In 1997, the U.S. Geological Survey (USGS) began an assessment of the lower Tennessee River Basin as part of the National Water-Quality Assessment Program. Existing nutrient and sediment data from 1980 to 1996 were compiled, screened, and interpreted to estimate watershed inputs from nutrient sources, provide a general description of the distribution and transport of nutrients and sediments in surface water, and evaluate trends in nutrient and sediment concentrations in the lower Tennessee (LTEN) River Basin. Nitrogen inputs from major sources varied widely among tributary basins in the LTEN River Basin. Point source wastewater discharges contributed between 0 and 0.61 tons per square mile per year [(tons/mi 2 )/yr]. Of the nonpoint sources of nitrogen for which inputs were estimated (atmospheric deposition, nitrogen fixation, fertilizer application, and livestock waste) livestock waste contributed the largest input in about two-thirds (7 out of 11) of the tributary basins, and fertilizer application contributed the largest input in the remaining 4 basins. Nitrogen input from fertilizer application was the most variable spatially among the nonpoint sources of nitrogen, ranging from 1.5 to 23 (tons/mi 2 )/yr. Atmospheric deposition estimates varied the least from basin to basin, ranging from 1.6 to 2.0 (tons/mi 2 )/yr. Estimates of nitrogen input from livestock waste ranged between 2.0 to 13 (tons/mi 2 )/yr. The percentage of the input from each of these nonpoint sources that entered the surface-water system is not known. Wastewater discharge contributed between 0 and 0.14 (ton/mi 2 )/yr of phosphorus to tributary basins. Livestock waste contributed most of the input in 8 out of the 11 basins, and fertilizer application contributed the most in the remaining 3 basins. Estimates of phosphorus input for fertilizer application ranged from 0.35 to 5.1 (tons/mi 2 )/yr and from 0.62 to 4.3 (tons/mi 2 )/yr from livestock waste. Reservoirs on the main stem of the Tennessee River and on the Duck and Elk Rivers affect nutrient transport because hydrodynamic conditions in the reservoirs promote assimilation by aquatic plants and deposition of particulate matter. Observed decreases in total nitrite plus nitrate and dissolved-orthophosphorus concentrations in reservoirs or at sites downstream of reservoirs during summer months were probably related to seasonality of plant growth. Nutrient and sediment data used to estimate annual instream loads and yields were compiled from various water-quality monitoring programs and represent the best available data in the LTEN River Basin, but these data have several characteristics that limit accuracy of load estimates. Many of the monitoring programs were not designed with the objective of annual load estimation, and data representing storm transport are, therefore, sparse; sampling and analytical methods varied through time and among the monitoring programs, hampering spatial and temporal comparisons. The load estimates computed from these data are useful for evaluating broad spatial patterns of instream load, and comparisons of instream load to inputs, but may not be sufficiently accurate for local-scale evaluations of water quality. Estimates of the mean annual instream load of total nitrogen entering (Chattanooga, Tenn.) and leaving (Paducah, Ky.) the LTEN River Basin were 29,000 and 60,000 tons per year (tons/yr), respectively. These estimates represent a gain of 31,000 tons/yr, on average, across the area (18,930 mi 2 ) between these inlet and outlet sites. The sum of the mean annual instream load from gaged tributaries to the main stem within the study unit was 14,000 tons/yr; however, this number cannot be directly compared with the gain between the inlet and outlet sites because (1) the gaged area represents only 30 percent of the total area and (2) the period of record at many tributary sites did not correspond with the period of record at the inlet or outlet sites. Estimates of mean annual instream load of total phosphorus at the inlet and outlet sites of the LTEN River Basin were 1,300 and 5,000 tons/yr, respectively, representing a gain of 3,700 tons/yr, on average, across the study unit. The sum of the gaged tributary load, representing only 28 percent of the area contributing to the main stem, was 4,300 tons/yr. Although this number cannot be closely compared with the gain throughout the study unit, for the same reasons given for total nitrogen, a general comparison suggests that the main stem of the Tennessee River and the tributary embayments along the main stem function as a sink for total phosphorus, removing a substantial amount from the water column through deposition or assimilation. The estimates of inputs can be compared and correlated with yields (area-normalized instream loads); significant correlations between estimates of inputs and yields might be useful as predictive tools for instream water quality where monitoring data are not available. Yields of nitrogen correlated moderately well with inputs from nonpoint sources, based on 1992 estimates. Nitrogen yield was highest [3.5 (tons/mi 2 )/yr] for Town Creek, for which the balance of nonpoint-source inputs to agricultural lands (fertilizer application plus nitrogen fixation plus livestock waste minus harvest) was also the highest [15 (tons/mi 2 )/yr]. Nitrogen yield was low [1.0 (tons/mi 2 )/yr] for the Buffalo River, for which the balance of agricultural nonpoint-source input was correspondingly low [3.2 (tons/mi 2 )/yr, the second lowest]. Correlation of wastewater discharge with yield was poor, and contrasted with the significant correlation between wastewater discharge and median nitrogen concentration during low streamflow. The poor correlation between wastewater discharge and annual yield was expected, however, as wastewater discharge is a small fraction compared with annual yield. In contrast with nitrogen, phosphorus yield did not correlate well with any estimated inputs or land-use types for the tributary basins. Phosphorus yield was highest [1.1 and 0.93 (tons/mi 2 )/yr] at two sites along the Duck River and at Elk River near Prospect [0.89 (ton/mi 2 )/yr]; however, estimates of inputs at these sites were in the middle of their respective ranges. The influence of the outcrop of phosphatic limestone formations of the brown-phosphate districts in the lower Duck and lower Elk River Basins might be responsible for the poor correlation between estimated inputs and yields of phosphorus. The outcrop pattern of these phosphatic limestones are an important factor to consider as regional boundaries are established for attainable, region-specific water-quality criteria for total phosphorus. Estimates of sediment input from cropland soil erosion in 1992 ranged from 51 to 540 (tons/mi 2 )/yr among the major hydrologic units in the LTEN River Basin. Information was not available to estimate this input for individual tributaries. Sediment yield estimates ranged from 65 to 263 (tons/mi 2 )/yr for the three tributary monitoring basins for which instream data were available, and from 17 to 26 (tons/mi 2 )/yr for the Tennessee River at South Pittsburg and at Pickwick Landing Dam, respectively. Lower sediment yields for the main stem sites compared with the tributary sites is probably due to sediment deposition in the main stem of the Tennessee River and tributary embayments along the main stem. Most of the significant trends in nutrient concentrations from about 1985 to about 1995 were decreasing trends, except for total nitrite plus nitrate, which increased at one site on the Elk River. The spatial distribution of decreasing trends of total nitrogen and total ammonia corresponds with the spatial variation among basins in wastewater loading rate. The time period of observed trends corresponds to the period of improvements in municipal treatment, thus decreases in wastewater effluent concentrations of nitrogen might be responsible for the decreasing trend in instream concentrations at these sites. Concentrations of total phosphorus did not decrease during this period at these sites, as might have been expected considering the reductions in wastewater input of phosphorus during this period.

Alabama, Georgia, Kentucky, Mississippi, Tennessee↗
USGS2022

Microcontinent breakup and links to possible plate boundary reorganization in the northern Gulf of California, México

Faults on microcontinents record the dynamic evolution of plate boundaries. However, most microcontinents are submarine and difficult to study. Here, we show that the southern part of the Isla Ángel de la Guarda (IAG) microcontinent, in the northern Gulf of California rift, is densely faulted by a late Quaternary-active normal fault zone. To characterize the onshore kinematics of this Almeja fault zone, we integrated remote fault mapping using high-resolution satellite- and drone-based topography with neotectonic field-mapping. We produced 13 luminescence ages from sediment deposits offset or impounded by faults to constrain the timing of fault offsets. We found that north-striking normal faults in the Almeja fault zone continue offshore to the south and likely into the nascent North Salsipuedes basin southwest of IAG. Late Pleistocene and Holocene luminescence ages indicate that the most recent onshore fault activity occurred in the last ∼50 kyr. These observations suggest that the North Salsipuedes basin is kinematically linked with and continues onshore as the active Almeja fault zone. We suggest that fragmentation of the evolving IAG microcontinent may not yet be complete and that the Pacific-North America plate boundary is either not fully localized onto the Ballenas transform fault and Lower Delfin pull-apart basin or is in the initial stage of a plate boundary reorganization.

Gulf of California↗
USGS2013

Tracking sedimentation from the historic A.D. 2011 Mississippi River flood in the deltaic wetlands of Louisiana, USA

Management and restoration of the Mississippi River deltaic plain (southern United States) and associated wetlands require a quantitative understanding of sediment delivery during large flood events, past and present. Here, we investigate the sedimentary fingerprint of the 2011 Mississippi River flood across the Louisiana coast (Atchafalaya Delta, Terrebonne, Barataria, and Mississippi River Delta basins) to assess spatial patterns of sedimentation and to identify key indicators of sediment provenance. The sediment deposited in wetlands during the 2011 flood was distinguished from earlier deposits based on biological characteristics, primarily absence of plant roots and increased presence of centric (planktonic) diatoms indicative of riverine origin. By comparison, the lithological (bulk density, organic matter content, and grain size) and chemical (stable carbon isotopes of bulk organic matter) properties of flood sediments were nearly identical to the underlying deposit. Flood sediment deposition was greatest in wetlands near the Atchafalaya and Mississippi Rivers and accounted for a substantial portion (37% to 85%) of the annual accretion measured at nearby monitoring stations. The amount of sediment delivered to those basins (1.1–1.6 g cm −2 ) was comparable to that reported previously for hurricane sedimentation along the Louisiana coast (0.8–2.1 g cm −2 ). Our findings not only provide insight into how large-scale river floods influence wetland sedimentation, they lay the groundwork for identifying previous flood events in the stratigraphic record.

Louisiana↗
USGS2006

High-resolution chirp seismic reflection data acquired from the Cap de Creus shelf and canyon area, Gulf of Lions, Spain in 2004

Seismic reflection data were collected from the Cap de Creus shelf and canyon in the southwest portion of the Gulf of Lions in October 2004. The data were acquired using the U.S. Geological Survey`s (USGS) high-resolution Edgetech CHIRP 512i seismic reflection system aboard the R/V Oceanus. Data from the shipboard 3.5 kHz echosounder were also collected but are not presented here. The seismic reflection data were collected as part of EuroSTRATAFORM funded by the Office of Naval Research. In October 2004, more than 200 km of high resolution seismic reflection data were collected in water depths ranging 30 m - 600 m. All data were recorded with a Delph Seismic PC-based digital recording system and processed with Delph Seismic software. Processed sections were georeferenced into tiff images for digital archive, processing and display. Penetration ranged 20-80 m. The data feature high quality vertical cross-section imagery of numerous sequences of Quaternary seismic stratigraphy. The report includes trackline maps showing the location of the data, as well as both digital data files (SEG-Y) and images of all of the profiles. The data are of high quality and provide new information on the location and thickness of sediment deposits overlying a major erosion surface on the Cap de Creus shelf; they also provide new insight into sediment processes on the walls and in the channel of Cap de Creus Canyon. These data are under study by researchers at the US Geological Survey, the University of Barcelona, and Texas A and M University. Copies of the data are available to all researchers.

Open-File Report↗
USGS2021

Historical floods and geomorphic change in the lower Little Colorado River during the late 19th to early 21st centuries

The Little Colorado River is a major tributary to the Colorado River with a confluence at the boundary between Marble and Grand Canyons within Grand Canyon National Park, Arizona. The bedrock gorge of the lower Little Colorado River is home to the largest known population of Gila cypha (humpback chub), an endangered fish endemic to the Colorado River Basin. Channel conditions might affect the spawning success of the humpback chub. Perennial base flow in the lower Little Colorado River deposits travertine, which forms dams and cascades. Geomorphic change in the lower Little Colorado River is controlled by the growth and collapse of travertine dams, debris flows from tributaries, and reworking of dams and debris fans by Little Colorado River floods. A study was conducted by the U.S. Geological Survey, in cooperation with the Glen Canyon Dam Adaptive Management Program and the U.S. Fish and Wildlife Service, to document historical floods and geomorphic change in the lower Little Colorado River. For this study, we used historical and gaging records and hydraulic modeling of surveyed high-water marks from historical Little Colorado River floods to construct a peak-flow history of the lower Little Colorado River. We analyzed base-flow longitudinal profiles and historical photographs to determine changes in the longitudinal profile of the lower Little Colorado River from 1909 to 2019. The peak-flow magnitudes and the frequency of larger floods have declined since the late 1800s, and the longitudinal profile of the Little Colorado River has substantially changed between 1909 and 2019. Aggradation of as much as 6 meters in some reaches occurred between 1926 and 1992, mostly before the 1950s. This aggradation was caused largely by the documented growth of travertine dams continuing through at least 2013 at several locations. Other reaches were incised by as much as 10 meters between 1926 and 1992, but mostly before the 1950s, largely from the breaching of travertine dams. Travertine dams in the Little Colorado River have survived large flooding events and then later collapsed during floods of lower streamflow or even periods of base flow. The decline in peak-flow magnitude and frequency has changed the dominant geomorphic processes in this formerly dynamic reach. Large incision events have not been documented since the early 1950s; for this reason, the reach has only aggraded or remained stable since that time. This loss of geomorphic disturbance has likely affected, and will likely continue to affect, the spawning habitat of the endangered humpback chub in the lower Little Colorado River.

Arizona, Utah, New Mexico, Utah↗
USGS2014

The global age distribution of granitic pegmatites

An updated global compilation of 377 new and previously published ages indicates that granitic pegmatites range in age from Mesoarchean to Neogene and have a semi-periodic age distribution. Undivided granitic pegmatites show twelve age maxima: 2913, 2687, 2501, 1853, 1379, 1174, 988, 525, 483, 391, 319, and 72 Ma. These peaks correspond broadly with various proxy records of supercontinent assembly, including the age distributions of granites, detrital zircon grains, and passive margins. Lithium-cesium-tantalum (LCT) pegmatites have a similar age distribution to the undivided granitic pegmatites, with maxima at 2638, 1800, 962, 529, 485, 371, 309, and 274 Ma. Lithium and Ta resources in LCT pegmatites are concentrated in the Archean and Phanerozoic. While there are some Li resources from the Proterozoic, the dominantly bimodal distribution of resources is particularly evident for Ta. This distribution is similar to that of orogenic gold deposits, and has been interpreted to reflect the preservation potential of the orogenic belts where these deposits are formed. Niobium-yttrium-fluorine (NYF) pegmatites show similar age distributions to LCT pegmatites, but with a strong maximum at ca. 1000 Ma.

Canadian Mineralogist↗
USGS2008

A 26 million year gap in the central Arctic record at the greenhouse-icehouse transition: Looking for clues

The Cenozoic record of the Lomonosov Ridge (central Arctic Ocean) recovered during Integrated Ocean Drilling Program (IODP) Expedition 302 revealed an unexpected 26 Ma hiatus, separating middle Eocene (∼44.4 Ma) from lower Miocene sediments (∼18.2 Ma). To elucidate the nature of this unconformity, we performed a multiproxy palynological (dinoflagellate cysts, pollen, and spores), micropaleontological (siliceous microfossils), inorganic, and organic (Tetra Ether Index of lipids with 86 carbon atoms (TEX 86 ) and Branched and Isoprenoid Tetraether (BIT)) geochemical analysis of the sediments from ∼5 m below to ∼7 m above the hiatus. Four main paleoenvironmental phases (A–D) are recognized in the sediments encompassing the unconformity, two below (A–B) and two above (C–D): (A) Below the hiatus, proxies show relatively warm temperatures, with Sea Surface Temperatures (TEX 86 ‐derived SSTs) of about 8°C and high fresh to brackish water influence. (B) Approaching the hiatus, proxies indicate a cooling trend (TEX 86 ‐derived SSTs of ∼5°C), increased freshwater influence, and progressive shoaling of the Lomonosov Ridge drilling site, located close to or at sea level. (C) The interval directly above the unconformity contains sparse reworked Cretaceous to Oligocene dinoflagellate cysts. Sediments were deposited in a relatively shallow, restricted marine environment. Proxies show the simultaneous influence of both fresh and marine waters, with alternating oxic and anoxic conditions. Pollen indicates a relatively cold climate. Intriguingly, TEX 86 ‐derived SSTs are unexpectedly high, ∼15–19°C. Such warm surface waters may be partially explained by the ingression of warmer North Atlantic waters after the opening of the Fram Strait during the early Miocene. (D) Sediments of the uppermost interval indicate a phase of extreme oxic conditions, and a well‐ventilated environment, which occurred after the complete opening of the Fram Strait. Importantly, and in contrast with classical postrifting thermal subsidence models for passive margins, our data suggest that sediment erosion and/or nondeposition that generated the hiatus was likely due to a progressive shoaling of the Lomonosov Ridge. A shallow water setting both before and after the hiatus suggests that the Lomonosov Ridge remained at or near sea level for the duration of the gap in the sedimentary record. Interacting sea level changes and/or tectonic activity (possibly uplift) must be invoked as possible causes for such a long hiatus.

Paleoceanography↗
USGS2008

A Miocene to Pleistocene climate and elevation record of the Sierra Nevada (California)

Orographic precipitation of Pacific-sourced moisture creates a rain shadow across the central part of the Sierra Nevada (California) that contrasts with the southern part of the range, where seasonal monsoonal precipitation sourced to the south obscures this rain shadow effect. Orographic rainout systematically lowers the hydrogen isotope composition of precipitation (δ D ppt ) and therefore δ D ppt reflects a measure of the magnitude of the rain shadow. Hydrogen isotope compositions of volcanic glass (δ D glass ) hydrated at the earth's surface provide a unique opportunity to track the elevation and precipitation history of the Sierra Nevada and adjacent Basin and Range Province. Analysis of 67 well dated volcanic glass samples from widespread volcanic ash-fall deposits located from the Pacific coast to the Basin and Range Province demonstrates that between 0.6 and 12.1 Ma the hydrogen isotope compositions of meteoric water displayed a large (>40‰) decrease from the windward to the leeward side of the central Sierra Nevada, consistent with the existence of a rain shadow of modern magnitude over that time. Evidence for a Miocene-to-recent rain shadow of constant magnitude and systematic changes in the longitudinal climate and precipitation patterns strongly suggest that the modern first-order topographic elements of the Sierra Nevada characterized the landscape over at least the last 12 million years.

California, Nevada↗
USGS1989

Turbidity-current channels in Queen Inlet, Glacier Bay, Alaska

Queen Inlet is unique among Glacier Bay fjords because it alone has a branching channel system incised in the Holocene sediment fill of the fjord floor. Bathymetry and seismic-reflection profiles show that four channels begin on, or at the base of, the delta front of this marine-outwash fjord. By midpoint of the fjord, these channels have merged into one main channel that extends the length of the fjord. The main channel cuts deeply into the scarp that separates this hanging tributary from the West Arm of Glacier Bay. The Queen Inlet channel ends on the main fjord floor as several small distributaries that form part of a lobate-fan deposit. Sand from the channel and lobate fan, in contrast to fjord-floor mud, plus steep truncated channel walls indicate that turbidity currents created this apparently active channel system. Queen Inlet and other known channel-containing fjords are marine-outwash fjords; the tidewater glacial fjords do not have steep delta fronts on which slides are generated and may not have a sufficient reservoir of potentially unstable coarse sediment to generate channel-cutting turbidity currents. Presence or absence of channels, as revealed in the ancient rock record, may be one criterion for interpreting types of fjords.

Alaska↗
USGS2004

Precipitation; ground-water age; ground-water nitrate concentrations, 1995-2002; and ground-water levels, 2002-03 in Eastern Bernalillo County, New Mexico

The eastern Bernalillo County study area consists of about 150 square miles and includes all of Bernalillo County east of the crests of the Sandia and Manzanita Mountains. Soil and unconsolidated alluvial deposits overlie fractured and solution-channeled limestone in most of the study area. North of Interstate Highway 40 and east of New Mexico Highway 14, the uppermost consolidated geologic units are fractured sandstones and shales. Average annual precipitation at three long-term National Oceanic and Atmospheric Administration precipitation and snowfall data-collection sites was 14.94 inches at approximately 6,300 feet (Sandia Ranger Station), 19.06 inches at about 7,020 feet (Sandia Park), and 23.07 inches at approximately 10,680 feet (Sandia Crest). The periods of record at these sites are 1933-74, 1939-2001, and 1953-79, respectively. Average annual snowfall during these same periods of record was 27.7 inches at Sandia Ranger Station, 60.8 inches at Sandia Park, and 115.5 inches at Sandia Crest. Seven precipitation data-collection sites were established during December 2000-March 2001. Precipitation during 2001-03 at three U.S. Geological Survey sites ranged from 66 to 94 percent of period-of-record average annual precipitation at corresponding National Oceanic and Atmospheric Administration long-term sites in 2001, from 51 to 75 percent in 2002, and from 34 to 81 percent during January through September 2003. Missing precipitation records for one site resulted in the 34-percent value in 2003. Analyses of concentrations of chlorofluorocarbons CFC-11, CFC-12, and CFC-113 in ground-water samples from nine wells and one spring were used to estimate when the sampled water entered the ground-water system. Apparent ages of ground water ranged from as young as about 10 to 16 years to as old as about 20 to 26 years. Concentrations of dissolved nitrates in samples collected from 24 wells during 2001-02 were similar to concentrations in samples collected from the same wells during 1995, 1997, and (or) 1998. Nitrate concentrations in two wells were larger than the U.S. Environmental Protection Agency primary drinking-water regulation of 10 milligrams per liter in 1998 and in 2001. Ground-water levels were measured during June and July 2002 and during June, July, and August 2003 in 18 monitoring wells. The median change in water level for all 18 wells was a decline of 2.03 feet.

New Mexico↗
USGS1956

Sedimentation and chemical quality of surface waters in the Wind River basin, Wyoming

This report gives results of an investigation by the U. S. Geological Survey of chemical quality of surface waters and sedimentation in the Wind River Basin, Wyo. The sedimentation study was begun in 1946 to determine the quantity of sediment that is transported by the streams in the basin; the probable sources of the sediment; the effect of large irrigation projects on sediment yield, particularly along Fivemile Creek; and the probable specific weight of the sediment when initially deposited in a reservoir. The study of the chemical quality of the water was begun in 1945 to obtain information on the sources, nature, and amounts of dissolved material that is transported by streams and on the suitability of the waters for different uses. Phases of geology and hydrology pertinent to the sedimentation and chemical quality were studied. Results of the investigation through September 30, 1952, and some special studies that were made during the 1953 and 1954 water years are reported. The rocks in the Wind River Basin are granite, schist, and gneiss of Precambrian age and a thick series of sedimentary strata that range in age from Cambrian to Recent. Rocks of Precambrian and Paleozoic age are confined to the mountains, rocks of Mesozoic age crop out along the flank of the Wind River and Owl Creek Mountains and in denuded anticlines in the floor of the basin, and rocks of Tertiary age cover the greater part of the floor of the basin. Deposits of debris from glaciers are in the mountains, and remnants of gravel-capped terraces of Pleistocene age are on the floor of the basin. The lateral extent and depth of alluvial deposits of Recent age along all the streams are highly variable. The climate of the floor of the basin is arid. The foothills probably receive a greater amount of intense rainfall than the areas at lower altitudes. Most precipitation in the Wind River Mountains falls as snow. The foothill sections, in general, are transitional zones between the cold, humid climate of the high mountains and the warmer, drier climate of the basin floor. Average annual runoff in the basin is about 3.6 inches on the basis of adjusted streamflow records for the Bighorn River near Thermopolis. Runoff from the mountains is high and is mostly from melting of snow and from spring and early summer rains. It does not vary greatly from year to year because annual water losses are small in comparison to annual precipitation. In the areas on the floor of the basin, where runoff is low, the runoff is mostly the result of storms in late spring and early summer. The annual water losses nearly equal the annual precipitation; therefore, runoff is extremely variable, in terms of percentage changes, from year to year and from point to point during any 1 year.

Water Supply Paper↗
USGS2004

Contaminant trends in reservoir sediment cores as records of influent stream quality

When reconstructing water-quality histories from lake and reservoir cores, it is sometimes assumed that the chemical signatures in the cores reflect historical water quality in the influent streams. To investigate this assumption, concentrations of metals, PAHs, and organochlorine compounds in sediment cores were compared to those associated with an influent-stream suspended sediment for three reservoirs in Fort Worth, TX, and two reservoirs in Boston, MA, U.S.A., and interpreted in light of land-use and regulation histories. In evaluating relations between suspended sediments and cores, three levels of preservation were indicated: (1) influent concentrations and historical trends are preserved in cores (metals at all sites; some organic contaminants at some sites); (2) some loss occurs during transport and initial deposition but relative historical trends are preserved in cores (some organic contaminants at some sites); and (3) neither stream concentrations nor relative historical trends are preserved (dieldrin and p,p???-DDT). The degree of preservation of influent concentration histories varied between lakes, particularly for PAHs. The results support the use of sediment cores to infer streamwater-quality histories for many contaminants but indicate that reservoir-bottom sediment samples might underestimate concentrations of organic contaminants in some streams.

Environmental Science & Technology↗
USGS2013

A record of large earthquakes during the past two millennia on the southern Green Valley Fault, California

We document evidence for surface-rupturing earthquakes (events) at two trench sites on the southern Green Valley fault, California (SGVF). The 75-80-km long dextral SGVF creeps ~1-4 mm/yr. We identify stratigraphic horizons disrupted by upward-flowering shears and in-filled fissures unlikely to have formed from creep alone. The Mason Rd site exhibits four events from ~1013 CE to the Present. The Lopes Ranch site (LR, 12 km to the south) exhibits three events from 18 BCE to Present including the most recent event (MRE), 1610 ±52 yr CE (1σ) and a two-event interval (18 BCE-238 CE) isolated by a millennium of low deposition. Using Oxcal to model the timing of the 4-event earthquake sequence from radiocarbon data and the LR MRE yields a mean recurrence interval (RI or μ) of 199 ±82 yr (1σ) and ±35 yr (standard error of the mean), the first based on geologic data. The time since the most recent earthquake (open window since MRE) is 402 yr ±52 yr, well past μ~200 yr. The shape of the probability density function (pdf) of the average RI from Oxcal resembles a Brownian Passage Time (BPT) pdf (i.e., rather than normal) that permits rarer longer ruptures potentially involving the Berryessa and Hunting Creek sections of the northernmost GVF. The model coefficient of variation (cv, σ/μ) is 0.41, but a larger value (cv ~0.6) fits better when using BPT. A BPT pdf with μ of 250 yr and cv of 0.6 yields 30-yr rupture probabilities of 20-25% versus a Poisson probability of 11-17%.

California↗
USGS2016

Fluvial system response to late Pleistocene-Holocene sea-level change on Santa Rosa Island, Channel Islands National Park, California

Santa Rosa Island (SRI) is one of four east-west aligned islands forming the northern Channel Islands chain, and one of the five islands in Channel Islands National Park, California, USA. The island setting provides an unparalleled environment in which to record the response of fluvial systems to major changes of sea level. Many of the larger streams on the island occupy broad valleys that have been filled with alluvium and later incised to form steep- to vertical-walled arroyos, leaving a relict floodplain as much as 12–14 m above the present channel. The period of falling sea level between the end of the last interglacial highstand at ~ 80 ka and the last glacial lowstand at ~ 21 ka was marked by erosion and incision in the uplands and by deposition of alluvial sediment on the exposed marine shelf. Sea level rose relatively rapidly following the last glacial lowstand of − 106 m, triggering a shift from an erosional to a depositional sedimentary regime. Accumulation of sediment occurred first through vertical and lateral accretion in broad, shallow channels on the shelf. Channel avulsion and delta sedimentation produced widespread deposition, creating lobes or wedges of sediment distributed across relatively large areas of the shelf during the latest Pleistocene. Backfilling of valleys onshore (landward of present sea level) appears to have progressed in a more orderly and predictable fashion throughout the Holocene primarily because the streams were confined to their valleys. Vertical aggradation locally reduced stream gradients, causing frequent overbank flooding and lateral channel shift by meandering and/or avulsion. Local channel gradient and morphology, short-term climate variations, and intrinsic controls also affected the timing and magnitudes of these cut, fill, and flood events, and are reflected in the thickness and spacing of the episodic alluvial sequences. Floodplain aggradation within the valleys continued until at least 500 years ago, followed by intensive arroyo cutting that abandoned the relict floodplains, forming alluvial terraces. Sedimentary evidence points to overgrazing and drought, followed by catastrophic flooding, in the mid-nineteenth century as factors that may have accelerated and dramatically enhanced arroyo formation on the island.

California↗
USGS2007

Synthesis of age data and chronology for Florida Bay and Biscayne Bay cores collected for ecosystem history of South Florida’s estuaries project

210 Pb, 14 C, and pollen biostratigraphic data have been compiled and synthesized to develop age models for cores collected from Florida Bay and Biscayne Bay. These cores are being used to interpret the ecosystem history of south Florida’s estuaries by examining the physical, chemical, and biological record preserved within the cores. The beginning of the 20th century, which marks an important turning point for the natural vs. anthropogenically influenced ecosystem, has been identified based on at least two data points in ten cores. 210 Pb data alone are presented for an additional 38 cores. Age models for older sediments have been developed for seven cores. Comparison of pre-1900 and post-1900 records allows researchers to compare natural ecosystem changes to anthropogenic change. General patterns of sedimentation rates in Florida Bay and Biscayne Bay emerge from the data. Mid-bay mudbanks in both bays show more rapid rates of sedimentation, fewer signs of sediment disruption, and more internal consistency of sediments than cores located closer to shore. Nearshore cores indicate slower average rates of sedimentation, more disruption in the sedimentary sequences, and more indications of “old” carbon effects. Cores in close proximity to each other generally show very similar patterns of deposition, which indicates support for the age models.

Southern Florida↗
USGS2012

Foraminiferal repopulation of the late Eocene Chesapeake Bay impact crater

The Chickahominy Formation is the initial postimpact deposit in the 85km-diameter Chesapeake Bay impact crater, which is centered under the town of Cape Charles, Virginia, USA. The formation comprises dominantly microfossil-rich, silty, marine clay, which accumulated during the final ~1.6myr of late Eocene time. At cored sites, the Chickahominy Formation is 16.8-93.7m thick, and fills a series of small troughs and subbasins, which subdivide the larger Chickahominy basin. Nine coreholes drilled through the Chickahominy Formation (five inside the crater, two near the crater margin, and two ~3km outside the crater) record the stratigraphic and paleoecologic succession of 301 indigenous species of benthic foraminifera, as well as associated planktonic foraminifera and bolboformids. Two hundred twenty of these benthic species are described herein, and illustrated with scanning electron photomicrographs. Absence of key planktonic foraminiferal and Bolboforma species in early Chickahominy sediments indicates that detrimental effects of the impact also disturbed the upper oceanic water column for at least 80-100kyr postimpact. After an average of ~73kyr of stressed, rapidly fluctuating paleoenvironments, which were destabilized by after-effects of the impact, most of the cored Chickahominy subbasins maintained stable, nutrient-rich, low-oxygen bottom waters and interstitial microhabitats for the remaining ~1.3myr of late Eocene time.

Maryl;Virginia↗